feat(config): Phase 2 Configurable Output — vestige.toml + output profiles (v2.1.26)

Rebased on v2.1.25 merge/supersede and bumped the post-release metadata to v2.1.26 so this branch does not roll versions backward.

Adds local vestige.toml defaults, output profiles, and MCP response precedence for search, timeline, codebase context, and session context.

Verified:
- cargo metadata --format-version 1 --locked --no-deps
- cargo test -p vestige-core config --no-fail-fast
- cargo test -p vestige-mcp config --no-fail-fast

docs/CONFIGURATION.md

@@ -50,6 +50,93 @@ Qwen3 currently uses Hugging Face Hub's Candle loader directly, so use the stand
 
 ---
 
+## Output Configuration (`vestige.toml`)
+
+> Added in **v2.1.26** (Roadmap Phase 2: Configurable Output).
+
+You can control the default shape and size of high-traffic MCP responses with an
+optional config file. It is **local-first** — no cloud service is involved — and
+**fully backward-compatible**: with no file present, Vestige behaves exactly as
+it did before.
+
+### Location
+
+The config file lives in the active Vestige data directory, alongside the
+database:
+
+```
+<data_dir>/vestige.toml      # e.g. ~/Library/Application Support/com.vestige.core/vestige.toml
+```
+
+The data directory is resolved with the same precedence as storage
+(`--data-dir` > `VESTIGE_DATA_DIR` > OS per-user data dir). A missing file, or a
+file with no recognized keys, falls back to built-in defaults. The parser is
+lenient: unknown keys and unknown sections are ignored, so the file can grow in
+future releases without breaking older binaries.
+
+### `[defaults]` table
+
+```toml
+[defaults]
+# Detail level for high-traffic tools: "brief" | "summary" | "full"
+detail_level = "summary"
+
+# Default result count for high-traffic tools (positive integer)
+limit = 10
+
+# Output profile: "lean" | "default" | "audit" | "research"
+profile = "default"
+```
+
+All three keys are optional. `detail_level` and `limit`, when set, override the
+selected profile's presets.
+
+### Output profiles
+
+A profile presets a coherent bundle of detail level, default limit, and whether
+scores and timestamps are included:
+
+| Profile | Detail | Default limit | Scores | Timestamps | Use when |
+|---------|--------|---------------|--------|------------|----------|
+| `lean` | `brief` | 5 | dropped | dropped | Context budget matters most |
+| `default` | `summary` | tool default | shown | shown | **Historical behavior (unchanged)** |
+| `audit` | `full` | tool default | shown | shown | Reviewing or debugging memory state |
+| `research` | `full` | 25 | shown | shown | Wide, detailed result sets |
+
+### Precedence
+
+Resolved per call, highest to lowest:
+
+1. **Explicit MCP parameter** (e.g. `detail_level` / `limit` on a `search`
+   call) — always wins.
+2. **`vestige.toml`** — the `[defaults]` keys and the selected profile.
+3. **Built-in default** — the `default` profile, identical to pre-v2.1.26
+   behavior.
+
+### Affected tools
+
+`search`, `memory_timeline`, `codebase` (`get_context`), and `session_context`
+resolve their default detail level and result limit through this config. Each of
+these tools also echoes the active `profile` in its response so you can confirm
+what was applied. Tools that take no `detail_level`/`limit` are unaffected.
+
+### Example: minimize context cost
+
+```toml
+[defaults]
+profile = "lean"
+```
+
+### Example: detailed audits without changing the profile
+
+```toml
+[defaults]
+detail_level = "full"
+limit = 50
+```
+
+---
+
 ## Command-Line Options
 
 ```bash